Since the discovery of P-glycoprotein (P-gp) in brain microvessels composing the human blood-brain barrier (BBB), ATPbinding
cassette (ABC) transporters have been recognized as bottlenecks in the development and delivery of neuropharmaceuticals. ABC
transporters are expressed predominately at the plasma luminal membrane of brain capillary endothelial cells. These ABC transporters
are responsible for the efflux of their substrates from the endothelial cells to the bloodstream against the concentration gradient and thus
limit the entry of some drugs within the central nervous system (CNS). Advanced quantitative molecular biology tools allowed gene and
protein quantification of the components of microvessels isolated from different species including human. Recently, positron emission
tomography using radiolabelled probes that are substrates of ABC transporters allowed the determination of their functional activity at
the human BBB. Here, we summarized new information regarding the relative expression, substrate recognition pattern for CNS drugs
and functional activity of ABC transporters that are quantitatively expressed at the human BBB.
Keywords: ATP-binding cassette transporters, blood-brain barrier, blood-cerebrospinal fluid barrier, P-glycoprotein, breast cancer resistance
protein, multidrug resistance protein.
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